Add config to disable schema dump after migration

* Add a config on Active Record named `dump_schema_after_migration`
* Schema dump doesn't happen if the config is set to false
* Set default value of the config to true
* Set config in generated production environment file to false
* Update configuration guide
* Update CHANGELOG

activerecord/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Add flag to disable schema dump after migration.
+
+    Add a config parameter on Active Record named `dump_schema_after_migration`
+    which is true by default. Now schema dump does not happen at the
+    end of migration rake task if `dump_schema_after_migration` is false.
+
+    *Emil Soman*
+
 *   Make sure transaction state gets reset after a commit operation on the record.
 
     If a new transaction was open inside a callback, the record was loosing track

activerecord/lib/active_record/core.rb

@@ -76,6 +76,15 @@ module ActiveRecord
       mattr_accessor :timestamped_migrations, instance_writer: false
       self.timestamped_migrations = true
 
+      ##
+      # :singleton-method:
+      # Specify whether schema dump should happen at the end of the
+      # db:migrate rake task. This is true by default, which is useful for the
+      # development environment. This should ideally be false in the production
+      # environment where dumping schema is rarely needed.
+      mattr_accessor :dump_schema_after_migration, instance_writer: false
+      self.dump_schema_after_migration = true
+
       # :nodoc:
       mattr_accessor :maintain_test_schema, instance_accessor: false
 

activerecord/lib/active_record/railties/databases.rake

@@ -34,7 +34,7 @@ db_namespace = namespace :db do
     ActiveRecord::Migrator.migrate(ActiveRecord::Migrator.migrations_paths, ENV["VERSION"] ? ENV["VERSION"].to_i : nil) do |migration|
       ENV["SCOPE"].blank? || (ENV["SCOPE"] == migration.scope)
     end
-    db_namespace['_dump'].invoke
+    db_namespace['_dump'].invoke if ActiveRecord::Base.dump_schema_after_migration
   end
 
   task :_dump do

guides/source/configuring.md

@@ -292,6 +292,12 @@ All these configuration options are delegated to the `I18n` library.
 
 * `config.active_record.maintain_test_schema` is a boolean value which controls whether Active Record should try to keep your test database schema up-to-date with `db/schema.rb` (or `db/structure.sql`) when you run your tests. The default is true.
 
+* `config.active_record.dump_schema_after_migration` is a flag which
+  controls whether or not schema dump should happen (`db/schema.rb` or
+  `db/structure.sql`) when you run migrations. This is set to false in
+  `config/environments/production.rb` which is generated by Rails. The
+  default value is true if this configuration is not set.
+
 The MySQL adapter adds one additional configuration option:
 
 * `ActiveRecord::ConnectionAdapters::MysqlAdapter.emulate_booleans` controls whether Active Record will consider all `tinyint(1)` columns in a MySQL database to be booleans and is true by default.

railties/CHANGELOG.md

@@ -1,3 +1,10 @@
+*   Set `dump_schema_after_migration` config values in production.
+
+    Set `config.active_record.dump_schema_after_migration` as false
+    in the generated `config/environments/production.rb` file.
+
+    *Emil Soman*
+
 *   Added Thor-action for creation of migrations.
 
     Fixes #13588 and #12674.

railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt

@@ -81,4 +81,9 @@ Rails.application.configure do
 
   # Use default logging formatter so that PID and timestamp are not suppressed.
   config.log_formatter = ::Logger::Formatter.new
+  <%- unless options.skip_active_record? -%>
+
+  # Do not dump schema after migrations.
+  config.active_record.dump_schema_after_migration = false
+  <%- end -%>
 end

railties/test/application/configuration_test.rb

@@ -781,5 +781,22 @@ module ApplicationTests
       assert_not Rails.configuration.respond_to?(:method_missing)
       assert Rails.configuration.respond_to?(:method_missing, true)
     end
+
+    test "config.active_record.dump_schema_after_migration is false on production" do
+      build_app
+      ENV["RAILS_ENV"] = "production"
+
+      require "#{app_path}/config/environment"
+
+      assert_not ActiveRecord::Base.dump_schema_after_migration
+    end
+
+    test "config.active_record.dump_schema_after_migration is true by default on development" do
+      ENV["RAILS_ENV"] = "development"
+
+      require "#{app_path}/config/environment"
+
+      assert ActiveRecord::Base.dump_schema_after_migration
+    end
   end
 end

railties/test/application/rake/migrations_test.rb

@@ -153,6 +153,37 @@ module ApplicationTests
            assert_match(/up\s+\d{3,}\s+Add email to users/, output)
         end
       end
+
+      test 'schema generation when dump_schema_after_migration is set' do
+        add_to_config('config.active_record.dump_schema_after_migration = false')
+
+        Dir.chdir(app_path) do
+          `rails generate model book title:string;
+           bundle exec rake db:migrate`
+
+          assert !File.exist?("db/schema.rb")
+        end
+
+        add_to_config('config.active_record.dump_schema_after_migration = true')
+
+        Dir.chdir(app_path) do
+          `rails generate model author name:string;
+           bundle exec rake db:migrate`
+
+          structure_dump = File.read("db/schema.rb")
+          assert_match(/create_table "authors"/, structure_dump)
+        end
+      end
+
+      test 'default schema generation after migration' do
+        Dir.chdir(app_path) do
+          `rails generate model book title:string;
+           bundle exec rake db:migrate`
+
+          structure_dump = File.read("db/schema.rb")
+          assert_match(/create_table "books"/, structure_dump)
+        end
+      end
     end
   end
 end